Porous carbon electrode substrate and its production method and carbon fiber paper

ABSTRACT

The present invention provides carbon fiber paper consisting of an organic high-molecular compound as a binder and carbon fibers, characterized in that the carbon fibers contain thin fibers with an average diameter smaller than 5 μm and an average fiber length of 3 to 10 mm; a porous carbon electrode substrate for a fuel cell having a thickness of 0.05 to 0.5 mm and a bulk density of 0.3 to 0.8 g/cm 3 , also having a bending strength of 10 MPa or higher and a deflection of 1.5 mm or more at the time of bending, measured by a three-point bending test in conditions of using a sample width of 1 cm, a strain rate of 10 mm/min, and a distance between supporting points of 2 cm; and a method of producing a porous carbon electrode substrate for a fuel cell by impregnating the carbon fiber paper with a thermosetting resin, curing the thermosetting resin by heating and pressing treatment, and then carbonizing the paper. The electrode substrate of the present invention is excellent in flexibility and bending strength and able to be rolled on a roll and thus has high productivity, and the carbon fiber paper of the present invention is suitable for producing the electrode substrate.

TECHNICAL FIELD

The present invention relates to carbon fiber paper and an electrodesubstrate for a fuel cell using the-paper and more particularly anelectrode substrate for a solid polymer electrolyte fuel cell and itsproduction method.

BACKGROUND ART

As compared with an electrode for a phosphoric acid fuel cell, anelectrode for a solid polymer electrolyte fuel cell is required to havegas diffusion-permeability, strength to be durable to handling,flexibility, strength to stand the compression at the time of electrodeproduction and electrode assembly, and the like. Further, since thesolid polymer electrolyte fuel cell is required to be small in size, ascompared with a phosphoric acid fuel cell, the electrode for it is alsorequired to be thin. As the electrode for such a solid polymerelectrolyte fuel cell, mainly used are those which are produced byforming paper from carbon short fibers, impregnating the paper with athermosetting resin, curing the resin, and then carbonizing theresultant paper, and in order to improve the productivity of a fuelcell, the electrode has to be flexible enough to be rolled in a roll.However, many electrodes ever made available are thick and mostly easilybroken when being bent. Further, since those conventional electrodeshave a few contacting points of carbon fibers, they have a problem thatthe conductivity becomes worse if the porosity is increased.

A porous carbon electrode-substrate provided with an improvedconductivity by mixing carbonaceous milled fibers is described inJapanese Patent Laid-Open No. 142068/1995, however the substrate is toothick in thickness and thus insufficient in flexibility to be used for asolid polymer electrolyte fuel cell.

Invention of a porous carbon plate and its production method isdescribed in Japanese Patent Laid-Open No. 157052/1997, the electrode ofthe invention has a low bulk density and therefore it cannot be saidthat the conductivity of the electrode is sufficient.

DISCLOSURE OF THE INVENTION

Objects of the present invention are to solve the above describedproblems and provide an electrode substrate for a fuel cell having highconductivity and flexibility, its production method, and carbon fiberpaper suitable for producing the electrode substrate.

The present invention provides carbon fiber paper consisting of anorganic high-molecular compound as a binder and carbon fibers, thecarbon fibers containing: thin fibers with an average diameter smallerthan 5 μm and an average fiber length of 3 to 10 mm.

In the carbon fiber paper of the present invention, the organichigh-molecular compound is preferably polyvinyl alcohol, and the organichigh-molecular compound is preferably pulp-like substances or shortfibers of an acrylonitrile type polymer. Further, the foregoing carbonfibers are preferably only of polyacrylonitrile type carbon fibers.Furthermore, the foregoing carbon fibers are preferably a mixture ofthin fibers with an average diameter larger than 3 μm and smaller than 5μm and an average fiber length of 3 to 10 mm and thick fibers with anaverage diameter not smaller than 5 μm and smaller than 9 μm and anaverage fiber length of 3 to 10 mm. It is also preferable for theforegoing carbon fibers to contain not less than 40% by mass of theforegoing thin fibers.

The present invention also provides a porous carbon electrode substratefor a fuel cell having a thickness of 0.05 to 0 5 mm and a bulk densityof 0.3 to 0.8 g/cm³, and also having a bending strength of 10 MPa orhigher and a deflection of 1.5 mm or more at the time of bending,measured by a three-point bending test in conditions of using a sampleof 1 cm width, a strain rate of 10 mm/min and a distance betweensupporting points of 2 cm.

The electrode substrate of the present invention preferably has a lengthof 1 m or larger and can be rolled around a roll with an outer diameterof 50 cm or smaller. Further, it is preferred that the electrodesubstrate contains carbon fibers, and the foregoing carbon fibers areonly of polyacrylonitrile type carbon fibers. Furthermore, it ispreferred that the electrode substrate contains carbon fibers, and thecarbon fibers are a mixture of thin fibers with an average diameterlarger than 3 μm and smaller than 5 μm and an average fiber length of 3to 10 mm and thick fibers with an average diameter not smaller than 5 μmand smaller than 9 Wm and an average fiber length of 3 to 10 mm. It isalso preferable for the electrode substrate to contain carbon fiberswhich contain not less than 40% by mass of the foregoing thin fibers inthe total carbon fibers.

The present invention also provides a method of producing a porouscarbon electrode substrate for a fuel cell by impregnating carbon fiberpaper consisting of an organic high-molecular compound as a binder andcarbon fibers with an average diameter smaller than 5 μm and an averagefiber length of 3 to 10 mm with a thermosetting resin, curing thethermosetting resin by heating and pressing treatment, and thencarbonizing the resultant paper.

In the production method of the present invention, it is preferable touse carbon fiber paper, among the above described carbon fiber paper,wherein the carbon fibers are made of a mixture of thin fibers with anaverage diameter larger than 3 μm and smaller than 5 μm and an averagefiber length of 3 to 10 mm and thick fibers with an average diameter notsmaller than 5 μm and smaller than 9 μm and an average fiber length of 3to 10 mm. Further, the foregoing heating and pressing treatment ispreferably carried out continuously in the whole length of the carbonfiber paper. Further, prior to the heating and pressing treatment, thecarbon fiber paper impregnated with the thermosetting resin ispreferably pre-heated. Furthermore, the heating and pressing treatmentis preferably carried out using a continuous type hot press machineequipped with a pair of endless belts, or the heating and pressingtreatment is preferably carried out using a continuous type hot rollpress machine. In the heating and pressing treatment, the pressureapplication is preferable to be carried out at a line pressure of1.5×10⁴ to 1 ×10⁵ N/m.

In the production method of the present invention, the foregoingcarbonization is preferably carried out continuously in the whole lengthof the carbon fiber paper. Further, the electrode substrate obtained bythe foregoing carbonization is preferable to be rolled around a rollwith the outer diameter of 50 cm or smaller. Furthermore, a conductivesubstance is preferably added to the foregoing thermosetting resin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a continuous type hot roll press machinesuitable to be used for the production method of the present invention,and

FIG. 2 shows an example of a continuous type hot press machine equippedwith a pair of endless belts and suitable to be used for the productionmethod of the present invention. 1 . . . resin-impregnated carbon fiberpaper, 2 . . . mold release agent-coated substrate, 3 a, 3 b . . .endless belts, 4 . . . preheating zone, 5 . . . heating and pressingzone

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will more particularly be described.

The carbon fiber paper of the present invention consists of carbonfibers containing thin carbon fibers with an average diameter smallerthan 5 μm and an average fiber length of 3 to 10 mm and an organichigh-molecular compound as a binder.

In the present invention, by using carbon short fibers with an averagediameter smaller than 5 μm, preferably larger than 3 μm and not largerthan 4.5 μm, the bending strength and the flexibility of the porouselectrode substrate can be improved. In the case of using only thickcarbon fibers with an average diameter larger than 5 μm, the flexibilitybecomes insufficient and the contacting points among fibers are toosmall in number, and the resistance of an electrode produced from suchcarbon fiber paper becomes too high. Further, by making an averagediameter larger than 3 μm, the carbon fiber paper is made dense and iscapable of preventing the decrease of gas permeability and therefore itis preferable.

Further, an average fiber length of the carbon fibers is preferable tobe 3 to 10 mm and further preferable to be 3 to 9 mm in terms of thestrength and the smoothness of a substrate. In the case where an averagefiber length is smaller than 3 mm, the fibers are less entangled toresult in decrease of the strength of the substrate. On the other hand,in the case of exceeding 10 mm, the dispersibility of fibers in adispersant is decreased to result in formation of uneven carbon fiberpaper.

The foregoing thin fibers with an average diameter smaller than 5 μm andan average fiber length of 3 to 10 mm are preferable to be not less than40% by mass in the total carbon fibers. That is, mixed carbon fibers canbe used as the carbon fibers of the present invention, the mixed carbonfibers being a mixture of 40% by mass or more of thin fibers with anaverage diameter smaller than 5 μm and an average fiber length of 3 to10 mm and 60% by mass or less of carbon fibers with an average diameternot smaller than 5 μm in the total carbon fibers. In order to maintainflexibility and high conductivity of an electrode substrate, it ispreferable to contain not less than 40% by mass of the foregoing thinfibers with an average diameter smaller than 5 μm in the mixed carbonfibers.

Other than the carbon fibers with an average fiber diameter smaller than5 μm and an average fiber length of 3 to 10 mm, carbon fibers with anaverage fiber diameter not smaller than 5 μm are preferable to be usedand carbon fibers with an average fiber diameter not smaller than 7 μmare further preferable to be used.

The carbon fibers contained in the carbon fiber paper are alsopreferably a mixture of thin fibers with an average diameter larger than3 μm and smaller than 5 μm and an average fiber length of 3 to 10 mm andthick fibers with an average diameter not smaller than 5 μm and smallerthan 9 μm and an average fiber length of 3 to 10 mm. The carbon fiberswith the thin diameter contribute to the improvement of flexibility andconductivity of an electrode, whereas the carbon fibers with the thickdiameter contribute to the improvement of dispersibility of the fibersubstrate and gas permeability. Consequently, carbon fiber paperproduced by properly mixing these fibers is provided with all of theabove described advantages and that is preferable.

The carbon fibers to be used in the present invention may be any ofpolyacrylonitrile type carbon fibers, pitch type carbon fibers, rayontype carbon fibers, and the like. However, polyacrylonitrile type carbonfibers, which have a relatively high mechanical strength are preferableand particularly, it is preferable that carbon fibers to be used aresolely polyacrylonitrile type carbon fibers.

The polyacrylonitrile type carbon fibers are produced using, as a rawmaterial, polymers mainly containing acrylonitrile. Practically, theyare carbon fibers obtained through a spinning process for spinningacrylonitrile type fibers, oxidizing process for converting the fibersinto oxidized fibers by heating them at 200 to 400° C. in airatmosphere, and carbonizing process for heating and carbonizing theresultant fibers at 300 to 2500° C. in an inert gas such as nitrogen,argon, helium, and the like, and preferably used as compositematerial-reinforcing fibers. Therefore, the fibers have high strength ascompared with other type carbon fibers and can be formed into carbonfiber paper with high mechanical strength.

The methods applicable for the paper-manufacturing method for producingthe carbon fiber paper include a wet method for producing paper bydispersing carbon short fibers in a liquid medium and a dry methodcomprising steps of dispersing carbon short fibers in air and depositingthe fibers. A proper amount of an organic high-molecular substance ispreferable to be added as a binder for binding the carbon fibers oneanother. In that way, the strength of carbon fiber paper is maintainedand separation of the carbon fibers from carbon fiber paper during theproduction process can be prevented and the orientation of the carbonfibers can be prevented from changing.

As the organic high-molecular compound, polyvinyl alcohol oracrylonitrile type polymers in pulp-like state or their short fibers arepreferable. The pulp-like materials or short fibers of the acrylonitriletype polymers are especially preferable since their carbonized materialscan function as conductors. Further, since the polyvinyl alcohol isexcellent in the contacting in the paper-manufacturing process, it ispreferable as a binder to suppress the separation of the carbon shortfibers. Further, the polyvinyl alcohol is almost all decomposed andvolatilized in the carbonization process in the final stage of producingthe electrode substrate and forms voids. Owing to the existence of thevoids, the water and gas permeability is improved and therefore, thepolyvinyl alcohol is preferable.

The pulp-like materials have a structure in which a large number offibrils with several μm or thinner diameter are branched from fibroustrunks, and in a sheet-like material produced from the pulp-likematerials, the fibers are efficiently entangled with one another andeven if a thin sheet-like material, the material has an advantage thatit is excellent in the handling property. The short fibers ofacrylonitrile type polymers can be obtained by cutting fiber threadsmade of acrylonitrile type-polymers or tows of the fibers in aprescribed length.

The content of the organic high-molecular compound in the carbon fiberpaper is preferably within a range from 5 to 40% by mass and morepreferably within a range from 15 to 30% by mass. In order to lower theelectric resistivity of the electrode substrate obtained by impregnatingthe carbon fiber paper with a resin and carbonizing the paper, it isbetter as the content is less, and the content is preferably not higherthan 40% by mass. From the viewpoint of keeping the strength and theshape of the carbon fiber paper, the content is preferably 5% by mass orhigher.

As a method for mixing the pulp-like materials or short fibers of theorganic high-molecular compound with carbon fibers, the followingmethods are preferable: a method for stirring and dispersing themtogether with carbon fibers in water and a method for directly mixingthem. In order to evenly disperse them, the method for dispersing anddiffusing in water is preferable.

After the carbon fiber paper is produced, the paper is hot-pressed byhot-press rolls to make the orientation and the thickness of the carbonfibers even and the fuzz which is characteristic of the carbon fiberscan be suppressed to a minimum. The heating temperature of the hot-pressrolls is preferably 100 to 150° C. and the pressure is preferably 0.5 to20 MPa.

The porous carbon electrode substrate for a fuel cell of the presentinvention is a-porous carbon electrode substrate for a fuel cell havingthe thickness of 0.05 to 0.5 mm, the bulk density of 0.3 to 0.8 g/cm³,and the bending strength of 10 MPa or higher measured by a three-pointbending test in conditions of using a sample width of 1 cm, a strainrate of 10 mm/min, and a distance between supporting points of 2 cm, anda deflection of 1.5 mm or more at the time of bending.

The porous carbon electrode substrate for a fuel cell comprisescarbonaceous materials such as carbon fibers as main constituentelements and is a substrate having water or gas permeability andconductivity sufficient to function as an electrode of a fuel cell. Asthe gas permeability of the porous electrode substrate, it is preferableto be 200 ml-mm/hr-cm²-mmAq or higher. As the conductivity, thethrough-plane resistivity is preferably 10 mΩ-cm² or lower in the casewhere the resistivity value is measured by applying electric currentwith current density of 10 mA/cm² while the electrode substrate beingsandwiched between copper plates and pressurized at 1 MPa from the upperand the lower sides of the copper plates.

The thickness of the porous carbon electrode substrate is needed to be0.05 to 0.5 mm from the viewpoint of the resistivity and preferable tobe 0.1 to 0.3 mm. If the thickness is thinner than 0.05 mm, the strengthin the thickness direction becomes low and it is insufficient to standhandling at the time of assembling a cell stack. On the other hand, ifexceeding 0.5 mm, the electric resistivity becomes high and the totalthickness becomes thick when a cell stack is assembled. The bulk densityis required to be 0.3 to 0.8 g/cm³ and preferable to be 0.4 to 0.7g/cm³. In the case where the bulk density is lower than 0.3 g/cm³ notonly the electric resistivity is increased but also satisfactoryflexibility cannot be obtained. On the other hand, in the case where thebulk density exceeds 0.8 g/cm³, the gas permeability is low and theperformance of a fuel cell is decreased.

The bending strength of the porous carbon electrode substrate of thepresent invention is required to be 10 MPa or higher, preferably 40 MPaor higher, in the case where it is measured in conditions of using asample width of 1 cm, a strain rate of 10 mm/min, and a distance betweensupporting points of 2 cm. If less than 10 MPa, the handling becomesdifficult and, for example, the substrate easily cracks at the time ofbeing rolled around a roll. By controlling the bending strength to be 10MPa or higher, cracking can be prevented at the time of bending theelectrode substrate. Moreover, the deflection at the time of bending is1.5 mm or more, preferably 2.0 mm or more. In the case where the bendingdeflection is less than 1.5 mm, the electrode substrate is easy to bebroken at the time of being continuously rolled around a roll and itbecomes difficult to produce and handle a long electrode substrate.

It is preferable for the porous carbon electrode substrate for fuelcells of the present invention to have length of 1 m or longer and beable to be rolled around a roll with the outer diameter of 50 cm orsmaller. If the electrode substrate is long and able to be rolled arounda roll, not only the productivity of the electrode substrate isincreased but also production of MEA (membrane/electrode assembly) in asuccessive process can continuously be carried out to contribute to theconsiderable cost down of a fuel cell. For that, the electrode substrateis preferable to be flexible enough to be rolled around a roll with theouter diameter at longest 50 cm, desirably 40 cm or smaller. The carbonelectrode substrate which is able to be rolled around a roll with theouter diameter of 50 cm or smaller is excellent in flexibility and inthrough-passing property in the MEA production process, which is asuccessive process of the rolling, and therefore, it is preferable.Further, if the electrode substrate can be rolled around a roll with theouter diameter of 50 cm or smaller, the carbon electrode substrate inthe form of a product can be compact and is advantageous in the packingand transportation cost. Also, in terms of prevention of breaking theelectrode substrate, the roll radius R (cm) is preferable to satisfy thefollowing inequality. $\begin{matrix}{R > \frac{x^{2} + 0.64}{0.8x}} & (1)\end{matrix}$wherein x denotes the deflection quantity (cm) at the moment ofoccurrence of rupture in bending in a three-point bending test.

In the present invention, carbon fiber paper containing thin carbonfibers with an average diameter smaller than 5 μm and an average fiberlength of 3 to 10 mm is impregnated with a thermosetting resin, thethermosetting resin is cured by heating and pressing, and then theresultant carbon fiber paper is carbonized to give the porous carbonelectrode substrate for a fuel cell.

The thermosetting resin to be employed for the present invention ispreferable a substance having adhesiveness or fluidity at roomtemperature and also able to remain as a conductive substance even aftercarbonization, and a phenol resin, a furan resin and the like areapplicable. A resol type phenol resin obtained by a reaction of phenolsand aldehydes in the presence of an alkaline catalyst can be used as theforegoing phenol resin. Further, a solid and thermally fusible novolaktype phenol resin produced by a reaction of phenols and aldehydes in thepresence of an acidic catalyst by a publicly known method may bedissolved and mixed in a resol type fluid phenol resin, and in this casea preferable one is a self-cross-linking type one containing a curingagent, for example, hexamethylenediamine.

As the phenols, usable ones are, for example, phenol, resorcin, cresol,xylol, and the like. As the aldehydes, usable ones are, for example,formalin, paraformaldehyde, furfural, and the like. Further, they may beused as mixtures. Commercially available products as phenol resins maybe used for them.

The preferable ratio of the resin in the resin-impregnated carbon fiberpaper of the present invention is 30 to 70% by mass. From the viewpointthat the structure of the porous carbon electrode substrate becomesdense and that the strength of the electrode substrate to be obtained ishigh, 30% by mass or higher is preferable. On the other hand, from theviewpoint that the porosity and gas permeability of the electrodesubstrate to be obtained can be kept excellent, 70% by mass or lower ispreferable. The term, resin-impregnated carbon fiber paper, means carbonfiber paper impregnated with a resin and not treated with heating andpressing yet, and in the case where a solvent is used for impregnationwith a resin, the term means the one from which the solvent is removed.

In the impregnation process of a thermosetting resin, a conductivesubstance maybe mixed with the thermosetting resin. As the conductivesubstance, examples are carbonaceous milled fibers, carbon black,acetylene black, isotropic graphite powder, and the like. The mixingratio of the conductive substance to be added in the resin is preferably1 to 10% by mass based on the resin. If the mixing ratio is less than 1%by mass, it is disadvantageous in that the effect on the conductivityimprovement is slight, and if the mixing ratio exceeds 10% by mass, itis disadvantageous in that the effect on the conductivity improvementtends to be saturated and that cost is increased.

Preferable methods for impregnating carbon fiber paper with a resin or amixture of a resin and a conductor are a method employing a squeezingapparatus and a method for overlaying a thermosetting resin film oncarbon fiber paper. The method employing a squeezing apparatus is amethod involving steps of immersing carbon fiber paper in a resinsolution or a resin mixed solution, applying the solution to the wholebody of the carbon fiber paper evenly by the squeezing apparatus, andadjusting the quantity of the solution by changing the distance betweenrolls of the squeezing apparatus. In the case of a relatively lowviscosity, a spraying method or the like is also applicable.

The method of using a thermosetting resin film is a method involvingsteps of once applying a thermosetting resin to mold release paper toobtain a thermosetting resin film and then laminating the film to carbonfiber paper and carrying out heating and pressing treatment to transferthe thermosetting resin.

The heating and pressing process in the present invention is preferableto be carried out continuously in the whole length of the carbon fiberpaper from the viewpoint of productivity. Further, prior to the heatingand pressing process, preheating is preferably carried out. In thepreheating process, the thermosetting resin is softened and in thesucceeding heating and pressing process, the thickness of an electrodesubstrate can be well controlled by pressing. An electrode substratewith the desired thickness and density can be obtained by pressing thepreheated resin-impregnated carbon fiber paper at a temperature higherthan the preheating temperature by 50° C. or more. In order to obtain anelectrode substrate with the desired thickness and density, a pluralityof resin-impregnated carbon fiber paper sheets may be piled and thensubjected to the heating and pressing treatment.

The foregoing heating and pressing treatment is preferably carried outusing a continuous type hot roll press machine or a continuous type hotpress machine equipped with a pair of endless belts. The lattercontinuous type hot press machine conveys a substrate by belts, andtensile force is scarcely applied to the substrate. Consequently, thesubstrate is hardly broken during the production and the machine isexcellent in terms of through-passing property. On the other hand, theformer continuous type hot roll press machine is simple in the structureand its running cost is low. The above described two heating andpressing manners are suitable methods for continuously curing the resinand preferable to be employed for production of the electrode substrateof the present invention.

The pressing pressure at the time of employing the foregoing continuoustype press machine is preferably 1.5×10⁴ to 1×10⁵ N/m. The heating andpressing treatment is a process necessary to sufficiently penetratefibers with the resin and to increase the bending strength. By pressingat the pressure of 1.5×10⁴ N/m or higher when thermally curing theresin, sufficient conductivity and flexibility can be achieved. On theother hand, by pressing at the pressure of 1×10⁵ N/m or lower, the vaporgenerated from the resin at the time of curing the resin cansufficiently be released to the outside and consequently occurrence ofcracking can be suppressed.

The heating temperature of the heating and pressing treatment ispreferably 140° C. or higher from the viewpoint of the hardeningtreatment duration and of the productivity and preferably 320° C. orlower from the viewpoint of the cost for the equipment such as heatingand pressing apparatus. Further preferably, the temperature is within arange of 160 to 300° C. The temperature of the foregoing preheating ispreferably within a range from 100 to 180° C.

In the present invention, it is preferable to continuously carry outcarbonization, which succeeds the resin curing, in the whole length ofthe carbon fiber paper. If the electrode substrate is long, not only theproductivity of the electrode substrate is increased, but also thesucceeding process of MEA production can continuously be carried out tocontribute to considerable cost down of a fuel cell. Practically, it ispreferable to carry out the carbonization by continuously firing thewhole length of the carbon fiber paper in a temperature range of 1,000to 3,000° C. in an inert atmosphere. In the carbonization of the presentinvention, pretreatment by pre-carbonizing in an inert atmosphere ofabout 300 to 800° C. range may be carried out before the carbonizationtreatment by firing in a temperature range of 1,000 to 3,000° C. in aninert atmosphere.

The electrode substrate finally obtained by the above described manneris preferable to be rolled around a roll with the outer diameter of 50cm or smaller and more preferable to be rolled around a roll with theouter diameter of 40 cm or smaller. If the electrode substrate can berolled around a roll with the outer diameter of 50 cm or smaller, theelectrode substrate in the form of a product can be compact and isadvantageous in the packing and transportation cost.

Hereinafter, the present invention will more particularly be describedaccording to examples.

The physical values and the like in the examples were measured by thefollowing methods.

1) Carbon Fiber Diameter

The diameter of carbon fibers was measured by helium-neon laser (SLB DIAMEASURING SYSTEM; produced by Anritsu Co.) as described in JIS R-7601.The measurement was carried out for 100 carbon fibers and an averagevalue was employed as an average diameter of the carbon fibers.

2) Thickness

The thickness was measured by employing a thickness measurementapparatus, Dial Thickness Gauge 7321 (produced by Mitsutoyo Co., Ltd.).The size of the measuring gauge was 10 mm in diameter and themeasurement pressure was constantly 1.5 kPa.

3) Bending strength of electrode substrate

The measurement was carried out by employing a bending strength testingapparatus. The distance between the supporting points was set to be 2cm, load was applied at strain rate of 10 mm/min, and the rupture loadof the pressing wedge was measured from the starting the application ofthe load to the moment when samples were ruptured and the bendingstrength was calculated according to the following equation.$\begin{matrix}{{{Bending}\quad{strength}\quad({MPa})} = \frac{{.3}\quad{PL}}{2\quad{Wh}^{2}}} & (2)\end{matrix}$

wherein P: rupture load (N); L: distance between supporting points (mm);W: width of a sample (mm); h: height of a sample (mm).

Incidentally, the value in the longitudinal direction was measured forcontinuous samples.

4) Deflection of Electrode Substrate

Measurement was carried out by employing a bending strength testingapparatus. The distance between the supporting points was set to be 2cm, load was applied at strain rate of 30 mm/min and the moving distanceof the pressing wedge was measured from the starting the application ofthe load to the moment when samples were ruptured, to measure thedeflection.

5) Gas Permeability Coefficient

According to JIS-P8117 and using a Gurley densometer, the time taken fora gas in 200 mm³ volume to pass through was measured to calculate thegas permeability coefficient.

6) Measurement of Through-lane Resistivity

The resistivity value was measured by applying electric current withcurrent density of 10 mA/cm² while a sample being sandwiched betweencopper plates and pressurized at 1 MPa from the upper and the lowersides of the copper plates and the piercing resistivity was calculatedbased on the following equation.

Trough-plane resistivity (Ω·cm²)=measured resistivity value (Ω)×samplesurface area (cm²) . . . (3)

EXAMPLE 1

Fiber bundles of polyacrylonitrile (PAN) type carbon fibers with anaverage fiber diameter of 4 μm were cut to obtain short fibers with anaverage fiber length of 3 mm.

Next, the short fiber bundles were spread in water and sufficientlydispersed, then short fibers of polyvinyl alcohol (PVA) (VBP 105-1 incut length 3 mm; produced by Kuraray Co., Ltd.) as a binder was evenlydispersed in 15% by mass in the total amount of the carbon fibers andPVA, paper manufacturing was manually carried out according to JISP-8209 method using a standard square sheet machine (No.2555 Standardsquare sheet machine; produced by Kumagai Riki Industry Co., Ltd.), andthe obtained paper was dried to obtain carbon fiber paper. PVA fiberswere in half-dissolved state and contacted the carbon fibers with oneanother. The areal weight of the obtained carbon fiber paper was 60g/cm².

The carbon fiber paper was immersed in an ethanol solution containing15% by mass of a phenol resin (Resitop PL-2211, produced by Gun-eiChemical Industry Co., Ltd.) and pulled out to impregnate 100 parts bymass of the carbon fibers with 100 parts by mass of the phenol resin andthen dried with a hot air, and then the resultant carbon fiber paper wassandwiched between fluorinated iron plates and kept in conditions of170° C. and 15 MPa for 15 minutes by a batch press apparatus to cure thephenol resin.

Successively, the obtained intermediate substrate was heated at 2,000°C. in a nitrogen gas atmosphere in a batch carbonization furnace for onehour to carbonize the substrate and obtain a porous carbon electrodesubstrate. Both of the bending strength and the deflection wereconsequently excellent.

The production conditions of carbon fiber paper sheets of the examplesand comparative examples are shown in Table 1: the production conditionsof electrode substrates in Table 2: and the evaluation results of theelectrode substrates in Table 3.

EXAMPLE 2

An electrode substrate was obtained in the same manner as the example 1except that the paper manufacturing was continuously carried out in thefollowing manner.

Fiber bundles of short carbon fibers were spread in water in a slurrytank and sufficiently dispersed, and then short fibers of polyvinylalcohol (PVA) as a binder (the same one used in the example 1) wasevenly dispersed and web was sent out. The sent out web was passedthrough short net plate and dried by a drier to obtain carbon fiberpaper with the length of 20 m. The obtained carbon fiber paper had theareal weight of 60 g/cm². Further the long carbon fiber paper was cutinto 25 cm length for the successive processes.

The electrode substrate of the present invention was provided withremarkably improved strength owing to the continuous paper-manufacturingand was also excellent in the deflection.

EXAMPLE 3

A long carbon fiber paper sheet was produced in the same manner as theexample 2, and the carbon fiber paper was impregnated with athermosetting resin by a dip-nip method. That is, the carbon fiber paperwas continuously sent to a tray containing a methanol solutioncontaining of 20% by weight of a phenol resin (Phenolite J-325, producedby Dainippon Ink and Chemicals, Inc.), the resin was squeezed by asqueezing apparatus, and then a hot air was continuously blown to dryand obtain resin-impregnated carbon fiber paper. In this case 100 partsby mass of carbon fibers were impregnated with 100 parts by mass of thephenol resin.

Next, the resin-impregnated carbon fiber paper was continuously heatedand pressed by a continuous type hot roll press machine illustrated inFIG. 1 to obtain resin-cured carbon fiber paper. That is, the abovedescribed resin-impregnated carbon fiber paper 1 was sent out the rollsand while being sandwiched between mold release agent-coated substrates2, the carbon fiber paper was sent to a preheating zone 4, successivelyto a heating and pressing zone 5, and then the mold release agent-coatedsubstrates 2 were removed and the obtained resin-cured carbon fiberpaper was rolled around a roll. In this case, the preheating temperaturein the preheating zone was 150° C. and the preheating duration was 5minutes and the temperature of the heating and pressing zone was 250° C.and the press pressure was 1.5×10⁴ N/m line pressure.

After that, the obtained resin-cured carbon fiber paper with the widthof 30 cm and the length of 20 m was cut at every 25 cm and fired in thesame manner as the examples 1 and 2 to obtain an electrode substrate.Both of the bending strength and the deflection were excellent.

EXAMPLE 4

An electrode substrate was obtained in the same manner as the example 3except that the press pressure of the roll press machine was heightenedto 7.5×10⁴ N/m of line pressure. Owing to the high press pressure, thesubstrate was made thin and the bending strength was high and thedeflection value was also high.

EXAMPLE 5

A resin-cured carbon fiber paper obtained by paper-manufacturing,impregnating with a resin, and subjecting to roll press in the samemanner as the example 4 was heated for 10 minutes in a continuous firingfurnace at 2,000° C. in a nitrogen gas atmosphere, without being cutinto pieces, to carbonize the carbon fiber paper and to continuouslyobtain a carbon electrode substrate with the length of 20 m, and thesubstrate was rolled around a cylindrical paper tube with the outerdiameter of 30 cm. The thickness was thin, the bending strength was highand the deflection value was also high.

EXAMPLE 6

After being subjected to continuous paper-manufacturing and impregnatingwith a resin process in the same manner as the example 3 except that theareal weight was controlled to be 100 g/m², the obtainedresin-impregnated carbon fiber paper was continuously subjected to hotpress by a continuous type hot press machine (a double belt pressmachine: DBP) equipped with a pair of endless belts as illustrated inFIG. 2 to obtain resin-cured carbon fiber paper. That is, the abovedescribed resin-impregnated carbon fiber paper 1 was placed between themold release agent-coated substrates 2 and were sent between continuesbelt apparatuses 3 a, 3 b, to a preheating zone 4, and successively to aheating and pressing zone 5. After that, as same in the case of the rollpress machine of FIG. 1, the mold release agent-coated substrates 2 wereremoved and the obtained resin-cured carbon fiber paper was rolledaround a roll. The continuous belt apparatuses 3 a, 3 b conveyedresin-impregnated carbon fiber paper 1 and the like by respectivelybeing rotated. In this case, the preheating temperature in thepreheating zone was 160° C. and the preheating duration was 5 minutesand the temperature of the heating and pressing zone was 280° C. and thepress pressure was 1.5×10⁴ N/m of line pressure. After that, theobtained resin-cured carbon fiber paper with the width of 30 cm and thelength of 20 m was cut at every 25 cm and fired in the same manner asthe examples 1 and 2 to obtain an electrode substrate. The substrate wassmooth, and both of the bending strength and the deflection wereexcellent.

EXAMPLE 7

An electrode substrate was obtained in the same manner as the example 6except that the press pressure of the double belt press (DBP) machinewas increased to 7.5×10⁴ N/m of line pressure. Owing to the high presspressure, the substrate was made thin and the bending strength was highand the deflection value was also high.

EXAMPLE 8

Continuous paper-manufacturing and impregnation with a resin werecarried out in the same manner as the example 7 except that carbon fiberpaper was continuously obtained while the areal weight being adjusted tobe 30 g/m². The heating and pressing process was carried out in the samemanner as the example 7 except two sheets of the obtainedresin-impregnated carbon fiber paper were piled in the manner that thesame paper-manufactured faces were set face to face in the inside at thetime of double belt press. The obtained substrate, without being cut,was subjected to precarbonization treatment by heating at 300 to 600° C.for 5 minutes in a nitrogen gas atmosphere in a furnace and thencarbonized by heating at 1,600 to 2,000° C. for 10 minutes in acontinuous carbonizing furnace to continuously obtain a carbon electrodesubstrate with the length of 20 m, and the substrate was rolled around apaper tube with the outer diameter of 30 cm. The obtained substrate wasnot at all warped and thin and provided with high bending strength and ahigh deflection value as well.

EXAMPLE 9

A carbon electrode substrate was obtained in the same manner as theexample 8 except that short fibers with an average fiber diameter of 4μm and an average fiber length of 6 mm were used instead of the shortfibers with an average fiber diameter of 4 μm and an average fiberlength of 3 mm. Although the dispersibility was relatively decreased,the strength, the deflection and the gas permeability were all togetherexcellent.

EXAMPLE 10

Fiber bundles of polyacrylonitrile (PAN) type carbon fibers with anaverage fiber diameter of 4 μm were cut to obtain short fibers with anaverage fiber length of 3 mm. On the other hand, fiber bundles of PANtype carbon fibers with an average fiber diameter of 7 μm were cut toobtain short fibers with an average fiber length of 6 mm. Next, theshort fiber bundles so mixed in the ratio of the short fibers with thefiber diameter of 4 μm and with the fiber diameter of 7 μm as 4 μm/7μm=8/11 were spread in water and sufficiently dispersed, and then shortfibers of polyvinyl alcohol (PVA) (the same one used in the example 1)as a binder was evenly dispersed in 5% by mass based on the total amountof the carbon fibers and PVA, and paper manufacturing was carried outaccording to JIS P-8209method using a standard square sheet machine (thesame one used in the example 1). Except that described above, theobtained paper was subjected to resin impregnation, batch press, andbatch carbonization to obtain an electrode substrate. Both of thebending strength and the deflection were consequently excellent.

EXAMPLE 11

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and impregnation with a resin, batchpress and batch carbonization were carried out in the same manner as theexample 2 except that the short carbon fibers and PVA were mixed in thesame ratio as that of the example 10 to obtain an electrode substrate.As compared with the results of the example 10, the bending strength wasremarkably increased and the deflection was also excellent.

EXAMPLE 12

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and continuous resin impregnation andresin drying, and then roll press and batch carbonization were carriedout in the same manner as the example 3 except that the short carbonfibers and PVA were mixed in the same ratio as that of the example 10 toobtain an electrode substrate. Both of the bending strength and thedeflection were excellent.

EXAMPLE 13

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and continuous resin impregnation andresin drying, and then roll press and batch carbonization were carriedout in the same manner as the example 4 except that the short carbonfibers and PVA were mixed in the same ratio as that of the example 10 toobtain an electrode substrate. Since pressing was carried out at ahigher pressure than that in the example 12, the electrode substrate wasthinner than the electrode substrate of the example 12, and bendingstrength and the deflection were higher than those of the substrate ofthe example 12.

EXAMPLE 14

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and continuous resin impregnation andresin drying, and then roll press and continuous carbonizing werecarried out in the same manner as the example 5 except that the shortcarbon fibers and PVA were mixed in the same ratio as that of theexample 10 to obtain an electrode substrate with the width of 30 cm andthe length of 20 m which was rolled on a cylindrical paper tube with theouter diameter of 30 cm. The electrode substrate was thin and thebending strength and the deflection of the substrate were high.

EXAMPLE 15

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and continuous resin impregnation andresin drying, and then double belt press (DBP) and batch carbonizationwere carried out in the same manner as the example 6 except that theshort carbon fibers and PVA were mixed in the-same ratio as that of theexample 10 to obtain an electrode substrate. Both of the bendingstrength and the deflection of the substrate were consequentlyexcellent.

EXAMPLE 16

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and continuous resin impregnation andresin drying, and double belt press (DBP) and batch carbonization werecarried out in the same manner as the example 7 except that the shortcarbon fibers and PVA were mixed in the same ratio as that of theexample 10 to obtain an electrode substrate. Since pressing was carriedout at a higher pressure than that in the example 15, the electrodesubstrate was thinner than the electrode substrate of the example 15 andbending strength and the deflection were higher than those of thesubstrate of the example 15.

EXAMPLE 17

Paper manufacturing was carried out by using a wet type continuouspaper-manufacturing apparatus, and continuous resin impregnation andresin drying, and double belt press (DBP) and continuous carbonizingwere carried out in the same manner as the example 8 except that theshort carbon fibers and PVA were mixed in the same ratio as that of theexample 10 to obtain an electrode substrate with the width of 30 cm andthe length of 20 m which was rolled on a cylindrical paper tube with theouter diameter of 30 cm. The obtained electrode substrate was completelyfree of warp and thin and provided with a high bending strength and ahigh deflection value.

EXAMPLE 18

A carbon electrode substrate was obtained in the same manner as theexample 17 except that short fibers with an average fiber diameter of 4μm and an average fiber length of 6 mm were used instead of the shortfibers with an average fiber diameter of 4 μm and an average fiberlength of 3 mm. Although the dispersibility was relatively decreased,the strength, the deflection and the gas permeability were all togetherexcellent.

EXAMPLE 19

A carbon electrode substrate was obtained in the same manner as theexample 1 except that polyacrylonitrile (PAN) type pulp was used as abinder instead of PVA when paper manufacturing. Although the bondingforce of the short carbon fibers was lower than that in the case ofusing PVA, both of the strength and the deflection were consequentlyexcellent.

EXAMPLE 20

A carbon electrode substrate was obtained in the same manner as theexample 1 except that carbon fiber paper was impregnated with a phenolresin using a resin solution of the phenol resin mixed with 1% by massof carbon black MA 100 (produced by Mitsubishi Chemical Industries Ltd.)versus the resin, at the time of resin impregnation. The conductivitywas a high value.

EXAMPLE 21

A carbon electrode substrate was obtained in the same manner as theexample 8 except that 35 parts by mass of carbon fiber paper wasimpregnated with 65 parts by mass of the phenol resin. Although the gaspermeability was slightly decreased, both of the bending strength andthe deflection were excellent.

EXAMPLE 22

After a long carbon fiber paper sheet was continuously obtained in thesame manner as the example 2, long phenol resin films with areal weightof 30 G/m² were obtained by applying a phenol resin (Phenolite 5900,produced by Dainippon Ink and Chemicals, Inc.) from which a solvent wasremoved to mold release paper sheets by a coater. The carbon fiber papersheet was sandwiched between the phenol resin films from the upper andthe lower sides to transfer the phenol resin to the carbon fiber papersheet, and then the carbon fiber paper sheet was subjected to degassingand rolled.

The obtained resin-impregnated carbon fiber paper was subjected to presscuring by a double belt machine and continuously carbonized in the samemanner as the example 8 except that the obtained resin-impregnatedcarbon fiber paper was not piled double, to obtain an electrodesubstrate with the width of 30 cm and the length of 20 m. The gaspermeability was excellent and both of the bending strength and thedeflection were excellent as well.

COMPARATIVE EXAMPLE 1

Carbon fiber paper of 60 g/m² was obtained by continuous papermanufacturing process in the same manner as the example 2 while usingonly PAN type short carbon fibers with an average fiber diameter of 7 μmas carbon fibers (the same ones as used in the example 10). Further, anelectrode substrate was produced from the carbon fibers by impregnationwith resin in the same manner as the example 3 and belt press andcontinuous carbonization in the same manner as the example 22. Althoughthe gas permeability coefficient was high, the deflection was low tocause cracking when the substrate was rolled around a roll.

COMPARATIVE EXAMPLE 2

Carbon fiber paper of 30 g/m² was obtained by continuous papermanufacturing process in the same manner as the example 8 while usingonly PAN type short carbon fibers with an average fiber diameter of 7 μmas carbon fibers as same in the comparative example 1. Successively, thecarbon fiber paper was subjected to impregnation with resin in the samemanner as the example 3, but without carrying out press, the resin wascontinuously cured at 180° C. and the carbon fiber paper wascontinuously carbonized as it was. The obtained electrode substrate wasvery brittle.

COMPARATIVE EXAMPLE 3

An electrode substrate was produced in the same manner as the example 1except that the pitch type carbon fibers with an average fiber length of11 mm were used instead of the PAN type carbon fibers. The bendingstrength was inferior and the electrode substrate was brittle. TABLE 1Methods for producing carbon fiber paper sheets in examples andcomparative examples A) CF of 4 μm B) CF of 7 μm Areal weigh diameter inFiber length diameter in Fiber length of carbon Paper- the total CF ofCF of 4 μm the total CF of CF of 7 μm Mixing ratio fiber papermanufacturing (% by mass) diameter (mm) (% by mass) diameter (mm) C)Binder by mass A/B/C (g/m²) method Example 1 100 3 — — PVA 85/0/15 60manual Example 2 100 3 — — PVA 85/0/15 60 continuous Example 3 100 3 — —PVA 85/0/15 60 continuous Example 4 100 3 — — PVA 85/0/15 60 continuousExample 5 100 3 — — PVA 85/0/15 60 continuous Example 6 100 3 — — PVA85/0/15 100 continuous Example 7 100 3 — — PVA 85/0/15 100 continuousExample 8 100 3 — — PVA 85/0/15 30 × 2 continuous Example 9 100 6 — —PVA 85/0/15 30 × 2 continuous Example 10 42 3 58 6 PVA 40/55/5 60 manualExample 11 42 3 58 6 PVA 40/55/5 60 continuous Example 12 42 3 58 6 PVA40/55/5 60 continuous Example 13 42 3 58 6 PVA 40/55/5 60 continuousExample 14 42 3 58 6 PVA 40/55/5 60 continuous Example 15 42 3 58 6 PVA40/55/5 100 continuous Example 16 42 3 58 6 PVA 40/55/5 100 continuousExample 17 42 3 58 6 PVA 40/55/5 30 × 2 continuous Example 18 42 6 58 6PVA 40/55/5 30 × 2 continuous Example 19 100 3 — — PAN 85/0/15 60 manualpulp Example 20 100 3 — — PVA 85/0/15 60 manual Example 21 100 3 — — PVA85/0/15 30 × 2 continuous Example 22 100 3 — — PVA 85/0/15 60 continuousComparative — — 100 6 PVA 0/85/15 60 continuous example 1 Comparative —— 100 6 PVA 0/85/15 30 continuous example 2 Comparative pitch 11 — — PVA85/0/15 60 manual example 3 100CF: carbon fibers

TABLE 2 Methods for producing electrode substrate in examples andcomparative examples Continuous Batch pressing Thermo- Heating andpressing line setting Resin/CF pressing pressure pressure ConductiveCarbonization resin mass ratio method (MPa) (×10⁴ N/m) substance methodRolled Example 1 PL2211 50/50 batch 15 — — batch — Example 2 PL221150/50 batch 15 — — batch — Example 3 PJ325 50/50 roll — 1.5 — batch —Example 4 PJ325 50/50 roll — 7.5 — batch — Example 5 PJ325 50/50 roll —7.5 — continuous 20 m Example 6 PJ325 50/50 DBP — 1.5 — batch — Example7 PJ325 50/50 DBP — 7.5 — batch — Example 8 PJ325 50/50 DBP — 7.5 —continuous 20 m Example 9 PJ325 50/50 DBP — 7.5 — continuous 20 mExample 10 PL2211 50/50 batch 15 — — batch Example 11 PL2211 50/50 batch15 — — batch — Example 12 PJ325 50/50 roll — 1.5 — batch — Example 13PJ325 50/50 roll — 7.5 — batch — Example 14 PJ325 50/50 roll — 7.5 —continuous 20 m Example 15 PJ325 50/50 DBP — 1.5 — batch — Example 16PJ325 50/50 DBP — 7.5 — batch — Example 17 PJ325 50/50 DBP — 7.5 —continuous 20 m Example 18 PJ325 50/50 DBP — 7.5 — continuous 20 mExample 19 PL2211 50/50 batch 15 — — batch — Example 20 PL2211 50/50batch 15 — CB 1% batch — Example 21 PJ325 65/35 DBP — 7.5 — continuous20 m Example 22 film 50/50 DBP — 7.5 continuous 20 m Comparative PJ32550/50 DBP — 7.5 — continuous 20 m Example 1 Comparative PJ325 50/50 — —— continuous 20 m Example 2 Comparative PL2211 50/50 batch 15 — — batch— example 3CB: carbon black

TABLE 3 Evaluation results of electrode substrates of examples andcomparative examples Trough-plane Gas Bulk Bending resistivity whenpermeability Thickness density strength Deflection pressed at(ml/hr/cm²/ (mm) (g/gm³) (MPa) (mm) 1 MPa (mΩ-cm²) mmAq) Example 1 0.170.39 11 2.4 3.98 2880 Example 2 0.17 0.48 60 2.4 3.98 1020 Example 30.17 0.45 50 2.1 3.75 1780 Example 4 0.15 0.55 60 2.5 3.66 820 Example 50.14 0.57 80 2.7 3.22 760 Example 6 0.27 0.49 55 1.6 6.07 500 Example 70.23 0.58 78 1.8 5.89 440 Example 8 0.14 0.61 130 2.9 3.12 720 Example 90.14 0.58 92 2.7 3.11 1000 Example 10 0.16 0.39 13 2.3 4.08 1760 Example11 0.17 0.48 63 2.5 3.78 1400 Example 12 0.17 0.45 52 2.0 3.9 1460Example 13 0.14 0.55 61 2.4 3.82 1000 Example 14 0.14 0.57 83 2.7 3.49960 Example 15 0.27 0.49 57 1.5 6.47 860 Example 16 0.23 0.58 79 1.76.19 560 Example 17 0.14 0.58 92 2.6 3.12 900 Example 18 0.14 0.58 822.8 3.42 2400 Example 19 0.17 0.41 11 2.3 3.21 2800 Example 20 0.18 0.4115 2.8 2.95 2600 Example 21 0.18 0.63 61 2.0 5.05 350 Example 22 0.180.55 82 2.0 4.23 370 Comparative 0.14 0.55 80 1.2 3.61 1500 example 1Comparative 0.14 0.29 4.5 1.2 2.55 3300 example 2 Comparative 0.18 0.348 2.4 3.21 6000 example 3* The distance between supporting points was kept constantly at 2 cm.

INDUSTRIAL APPLICABILITY

A porous carbon electrode substrate for a fuel cell of the presentinvention is a substrate excellent in flexibility, durable to bendingand able to be rolled around a roll, and thus having high productivity.Carbon fiber paper of the present invention is suitable for producingsuch an excellent electrode substrate. According to the productionmethod of the present invention for producing the porous carbonelectrode substrate for a fuel cell, such an excellent electrodesubstrate can be produced.

1-11. (canceled)
 12. A method of producing a porous carbon electrodesubstrate for a fuel cell by impregnating carbon fiber paper consistingof an organic high-molecular compound as a binder and carbon fibers withan average diameter smaller than 5 μm and an average fiber length of 3to 10 mm with a thermosetting resin; curing the thermosetting resin byheating and pressing treatment; and then carbonizing the paper.
 13. Themethod of producing a porous carbon electrode substrate for a fuel cellas claimed in claim 12, characterized in that said carbon fiber paper isthe carbon fiber paper as claimed in claim
 5. 14. The method ofproducing a porous carbon electrode substrate for a fuel cell as claimedin claim 12, characterized in that said heating and pressing treatmentis carried out continuously in a whole length of the carbon fiber paper.15. The method of producing a porous carbon electrode substrate for afuel cell as claimed in claim 12, characterized in that prior to saidheating and pressing treatment, the carbon fiber paper impregnated withthe thermosetting resin is pre-heated.
 16. The method of producing aporous carbon electrode substrate for a fuel cell as claimed in claim12, characterized in that said heating and pressing treatment is carriedout using a continuous type hot press machine equipped with a pair ofendless belts.
 17. The method of producing a porous carbon electrodesubstrate for a fuel cell as claimed in claim 12, characterized in thatsaid heating and pressing treatment is carried out using a continuoustype hot roll press machine.
 18. The method of producing a porous carbonelectrode substrate for a fuel cell as claimed in claim 12,characterized in that at the time of said heating and pressingtreatment, the pressure application is carried out at a line pressure of1.5×10⁴ to 1×10⁵ N/m.
 19. The method of producing a porous carbonelectrode substrate for a fuel cell as claimed in claim 12,characterized in that said carbonization is carried out continuously inthe whole length of the carbon fiber paper.
 20. The method of producinga porous carbon electrode substrate for a fuel cell as claimed in claim12, characterized in that the electrode substrate obtained by saidcarbonization is rolled around a roll with the outer diameter of 50 cmor smaller.
 21. The method of producing a porous carbon electrodesubstrate for a fuel cell as claimed in claim 12, characterized in thata conductive substance is added to said thermosetting resin.
 22. Themethod of producing a porous carbon electrode substrate for a fuel cellas claimed in claim 13, characterized in that said heating and pressingtreatment is carried out continuously in a whole length of the carbonfiber paper.
 23. The method of producing a porous carbon electrodesubstrate for a fuel cell as claimed in claim 13, characterized in thatprior to said heating and pressing treatment, the carbon fiber paperimpregnated with the thermosetting resin is pre-heated.
 24. The methodof producing a porous carbon electrode substrate for a fuel cell asclaimed in claim 13, characterized in that said heating and pressingtreatment is carried out using a continuous type hot press machineequipped with a pair of endless belts.
 25. The method of producing aporous carbon electrode substrate for a fuel cell as claimed in claim13, characterized in that said heating and pressing treatment is carriedout using a continuous type hot roll press machine.
 26. The method ofproducing a porous carbon electrode substrate for a fuel cell as claimedin claim 13 characterized in that at the time of said heating andpressing treatment, the pressure application is carried out at a linepressure of 1.5×10⁴ to 1×10⁵ N/m.
 27. The method of producing a porouscarbon electrode substrate for a fuel cell as claimed in claim 13,characterized in that said carbonization is carried out continuously inthe whole length of the carbon fiber paper.
 28. The method of producinga porous carbon electrode substrate for a fuel cell as claimed in claim13, characterized in that the electrode substrate obtained by saidcarbonization is rolled around a roll with the outer diameter of 50 cmor smaller.
 29. The method of producing a porous carbon electrodesubstrate for a fuel cell as claimed in claim 13, characterized in thata conductive substance is added to said thermosetting resin.